WASHINGTON—Fabric prints, knockoff styles and the slimming lines of a Kate Winslet-worn dress were all part of a vigorous Supreme Court debate Monday in a case about cheerleader uniforms, one that could have important implications for the fashion industry.

The high court spent an hour considering when the design elements of clothing can be eligible for copyright protection, an issue that required the justices to consider the qualities that make a cheerleading uniform what it is.